The recent image forming apparatus may be provided with a function of concealing information contained in image data before the image data is output as a printed document, for example, in order to prevent the illegal copy of a monetary document such as a paper currency or a security. When the image forming apparatus determines that the original document to be copied includes specific information, which can be only observed in the paper currency or the security, the image forming apparatus may conceal the information contained in the image data of the original document by printing the image data with the solid black image.
For example, as described in the Japanese Patent Application Publication No. 2000-232576, after converting the RGB image data of an original document to image data of uniform color spaces, a currency recognizing device determines whether the original document contains a specific image. When it is determined that the original document contains the specific image, an image processing apparatus paints the YMCK image data converted from the image data of uniform color spaces.
In another example, the Japanese Patent Application Publication No. 2006-262376 describes an image processing apparatus, which paints the YMCK image data converted from the image data of an original document when the image data contains a group of dot patterns indicating that the image data is a specific image. The color of the color material used for panting can be selected so as to make the consumption rate is kept uniform among a plurality of colors. In another example, the Japanese Patent Application Publication No. 2006-175031 describes an image processing apparatus, which converts RGB image data to YMCK image data, applies concealing processing to the YMCK image data, and stores the processed image data. Alternatively, the image processing apparatus of the Japanese Patent Application Publication No. 2000-175031 may apply concealing processing to the RGB image data, and stores the processed image data.
In another example, the Japanese Patent Application Publication No. 2006-287707 describes an image processing apparatus, which stores image data obtained by a scanner in a memory. When reading of an original document completes, the image data is read out from the memory, and is painted when the image data is detected to be a specific image. Alternatively, the image data may be printed when a predetermined lines of the image data is read. In such case, when the image data is detected to be the specific image, painting is performed on the image data while printing the image data.